The present invention relates to a headlamp for automotive vehicles.
Automotive vehicles, such as cars, are normally provided with main headlights which are constructed to emit a full beam image, or high beam image, and a dipped beam image, or low beam image. For at least 15 years, vehicles have been fitted with halogen headlamps in order to increase the light yield.
It is a generally known problem that while the full beam of a vehicle headlamp will illuminate the surroundings well ahead of the vehicle in darkness, the beam will also dazzle the occupants of any oncoming vehicle. On the other hand, whereas the dipped beam will not have the same dazzling effect on oncoming vehicles, it does not illuminate the surroundings ahead of the vehicle to a satisfactory extent. Normally, however, the extent of illumination afforded by a dipped beam is adequate enough to enable the driver to see the road sufficiently well to drive the vehicle.
However, the ability to discern roadside objects, such as road signs and other fixtures, or pedestrians etc., is greatly impaired when driving on dipped headlights rather than on full beam.
Since the illuminating lobe of a dipped headlight with appreciable light intensity, is not higher than about 0.5 to 1 meter above the road surface, the light reflected from the road sign or other roadside object is often too weak to be discerned readily by the occupants of the vehicle. The distances at which safety reflectors carried by pedestrians can be observed safely are also much shorter when the vehicle is on dipped headlights than when driven on full beam.
The light yield could be increased still further, by replacing the conventional halogen headlamps with gas discharge lamps.
One drawback with gas discharge lamps, however, is that their ignition time is of such long duration as to render it impossible to switch rapidly between full beam and dipped beam.
A progressively increasing desire in this respect is one of fitting to automotive vehicles lamps capable of emitting ultraviolet light. This light causes a large number of different colours to fluoresce to greater and lesser extents. In recent times it has become more and more usual to utilize so-called day-glow inks on signs etc., i.e. inks which when irradiated with ultraviolet light (UV) will transmit visible light. Roadside objects are today painted with such day-glow inks and paints. Furthermore, some emergency vehicles have broad strips painted thereon in day-glow colours. Light-coloured clothing will also fluoresce well when illuminated with ultraviolet light.
If it were possible for a vehicle to transmit ultraviolet light, it would render the painting of road signs, roadside demarcation posts, etc. with a fully or partially day-glow paint more viable than is now the case, from a road safety aspect.
However, as beforementioned, the use of gas discharge lamps which emit a high proportion of ultraviolet light is seriously encumbered by the long ignition times of such lamps.